1. Field of the Invention
The present invention relates to an actuator for use in an optical pickup, and more particularly, to the construction of a magnetic spring which acts in the focusing direction in an actuator of the type in which focusing and tracking are performed by sliding the lens in the axial direction and by rotating it about a shaft, respectively.
2. Description of the Prior Art
In an actuator of the type in which focusing and tracking are conducted by sliding a lens in the axial direction and rotating it about a shaft, respectively, it is common to use a rubber spring as a focusing spring. FIG. 2 shows an example of such a conventional actuator. In the Figure, one end of a rubber spring 21 is fixed to a pin 23 set up in a fixed portion such as a yoke, and the other end thereof is fixed through a pin 22 to an objective lens retaining tube 1 constituting a moving portion. In consequence, when the objective lens moves in the focusing direction indicated by A, the objective lens is retained by the resilient force of the rubber spring 21, thereby maintaining the focusing stability.
This conventional method of retention by a rubber spring, however, requires the provision of space for the rubber spring, and is therefore very inconvenient from the viewpoint of the desirability of reducing the size of the pickup, which has been requested more and more in recent years.
If the rubber spring is inaccurately mounted in such a way that it is disclosed, nonlinearity may be generated in the spring action. This makes the process of mounting the rubber spring very troublesome.
In addition, the rubber spring does not have good temperature characteristics due to the physical properties of its material, and is subjected to deterioration as its resonance frequency or sensitivity changes.